1. Field of the Invention
The present invention generally relates to computer storage system technology. More particularly, the present invention pertains to a method and apparatus for detecting an intermittent path between a host computer and a storage system.
2. Description of the Related Art
In modern computing systems, a host computer (e.g., a server) may be directly connected to a storage system in an arrangement known as Direct Attached Storage (DAS). The storage system may comprise a multitude of redundant storage arrays to promote high availability and robustness. A path is defined as a logical connection from the host computer to the storage system comprising the disk arrays. In other computing environments, the storage systems may be coupled to the host computer through a communications network in an arrangement known as a Storage Area Network (SAN). In such systems, the communications network is known as a SAN fabric that provides a plurality of paths from the host computer to the storage arrays.
In both DAS and SAN configurations, a large number of paths may exist; although, typically, a SAN configuration has substantially more complex interconnection configuration than a DAS. In either configuration there may be complex physical cabling arrangements. A loose connection of a cable connector can result in intermittent connectivity along a path. Each time a connector “breaks” a connection, the host computer is notified of a path failure. Such a path failure causes the host computer to search for a secondary path to the storage system. In a system that uses passive/active storage, upon a path failure, the host computer begins a fail-over process to avoid using the failed path. When the intermittent path again forms a path, the host computer may restore the connection (i.e., fail-back) through the original path. Upon another interruption on the intermittent path, the host computer will fail-over again and so on. Such repeated fail-over and fail-back processes or repeated searching for alternative paths detrimentally impacts the functionality of the host computer and its ability to utilize the storage system in an efficient manner.
Accordingly, there is a need in the art for a method and apparatus for detecting intermittent paths to a storage system such that these paths can be avoided until the path becomes stable.